The stress will begin in college. Whether it's a Ph.D. or M.D. that you're pursuing, you'll be busting your hump for at least eight years. Papers, presentations, and failed hypotheses will test your patience and pride. And depending on your specialty or research direction, it could be more than just eight years.
Then there's the stress of the actual job. Immunologists deal pretty directly with some nasty diseases, either by treating the people who come in with them or by researching for a cure. Either way, it'll feel like you're racing against the clock to solve a difficult problem. It might be stressful and frustrating. But we know you can handle it.